Effects of Shewanella putrefaciens on innate immunity and cytokine expression profile upon high stocking density of gilthead seabream specimens

• Innate immunity of gilthead seabream was studied under low and high stocking density.
• Pdp11 increase the innate immunity and the cytokine expression profile.
• Gilthead seabream seric bactericidal activity did not show effect against Pdp11.
• Pro-inflammatory cytokine profile is strongly modulated by Pdp11 and stress.

High stocking density increases the number of emerging diseases triggering economic losses worldwide. Probiotics provide an effective and natural solution for preventing some diseases through an improvement of innate immune system among others. In the present work dietary administration of the probiotic Shewanella putrefaciens (known as Pdp11) was evaluated under stress by high stocking density after 2 and 4 weeks of administration to gilthead seabream (Sparus aurata) specimens. Results showed an increase in cellular peroxidase and respiratory burst activity as well as a modulation of cytokine profile when Pdp11 was administered to fish reared at high stocking density. Overall, our results showed how Pdp11 is not only able to improve to some extent the cellular and humoral immunity but also to increase the gene expression profile of pro-inflammatory cytokines such as il1b or il6 in response to high stocking density in gilthead seabream. These findings may support the potential use of this probiotic as functional feed against stress in fish farms.